1. Field of the Invention
The present invention relates generally to a Wireless Local Area Network (WLAN) mesh network. More particularly, the present invention relates to a method and system for performing re-association due to the movement, such as, handover, of a mesh point in the network.
2. Description of the Related Art
A Local Area Network (LAN) is a set of personal terminals, main frames, and workstations connected to one another with a communication line of 300 meters or shorter. A LAN is also a high-speed communication network connected so that remotely installed equipment in which currents or radio signals between the personal terminals can be correctly delivered. For example, the equipment in the building of one institution can be efficiently shared by the entire staff. In the past, the wired networks that directly delivered the electric signals were mainly used as communication lines applied to the LAN. Due to the development of wireless protocols, the wired networks are increasingly replaced with wireless networks that deliver signals using radio waves. The LAN using the wireless network is generally called a Wireless Local Area Network (WLAN), or a wireless in-building information communication network, which is based on IEEE 802.11 proposed by the Institute of Electrical and Electronics Engineers (IEEE). The IEEE 802.11-based WLAN has grown at a fast rate in recent years, and is expected to make more rapid developments in the future due to its advantage of convenient network connection. As the demands for the high-speed wireless Internet increase rapidly, the existing WLAN system serves as an alternative to the infrastructure of the high-speed wireless public network.
The WLAN includes a plurality of access points (APs) connected via one distribution system (DS), and a plurality of stations (STAs) that receive services via the APs. Therefore, the AP serves as a bridge between terminals and the remainder of the network.
In a WLAN, the STA performs handover to a new AP from which it will newly receive the service when strength of a signal received from its current AP decreases due to its mobility. Therefore, in order to switch the service to the new AP, the STA needs authentication and re-association with the new AP. In this case, the STA performs handover from the old AP with which it has been communicating, to the new AP. The handover process will be described below with reference to FIG. 1.
FIG. 1 is a signaling diagram schematically illustrating a handover procedure due to the movement of an STA in a general WLAN.
Referring to FIG. 1, a procedure is shown in which an STA 100 moves from an old AP 140 to a new AP 130. The STA 100, due to the movement, performs a Probe phase for asking each individual AP its opinion on the possibility of handover success.
The STA 100 sends a Probe Request message to a plurality of unspecified APs 120 in steps 111 and 115. Upon receiving the Probe Request message, the APs 120 transmit a Probe Response message to the STA 100 in step 113 and 117. The phrase “receiving the Probe Request message” means that the corresponding AP is adjacent to the mobile station (STA), so the AP can be assumed to be a latent AP. The Probe phase is repeatedly performed for each individual channel. The process of performing the Probe phase by changing the channel is shown in steps 115 and 117.
The STA 100 generates a priority list of the APs through the Probe phase. AP priorities are determined using strengths of signals received from the APs, by way of example.
The STA 100 performs an Authentication phase with the latent APs according to the priority list in steps 119 and 121. The STA 100 can perform the Authentication phase of requiring delivery of a credential and other state information from the old AP 140, via the new AP 130.
Next, the STA 100 performs a Re-association phase. The handover can be achieved through the Re-association phase and an Inter-Access Point Protocol (IAPP). Delivery of the state information is performed by the IAPP. The state information commonly refers to information that facilitates access to the network and the information includes information on a client's position and several accountings.
The STA 100 performs the Re-association phase based on the priorities of the latent APs registered in the priority list generated in the Probe phase. The STA 100 then transmits a Re-association Request message to the new AP 130 in step 123. The new AP 130 then performs an IAPP procedure with the old AP 140 through the other APs in steps 125, 127, 129 and 131. Through this procedure, the new AP 130 receives a credential allocated to the mobile station and other state information.
In step 133, the new AP 130 sends a Re-association Response message to the mobile station in response to the Re-association Request message.
As described above, the conventional handover procedure starts when the mobile station sends a Probe Request message, and ends when the mobile station receives a Re-association Response message. As a result, the handover procedure suffers from a probe delay, an authentication delay, and a re-association delay. The probe delay occurs in the Probe phase, the authentication delay occurs in the Authentication phase, and the re-association delay occurs in the Re-association phase.
First, the probe delay occurs while the STA 100 transmits a Probe Request message and waits for a response thereto for each individual AP in each channel. The time for which the mobile station waits for the response in a particular channel after transmitting the Probe Request message is called a probe-wait delay. This is determined based on a time difference with the next transmitted Probe Request message. As a result, the traffic in the channels and timing of the Probe Response message may affect the probe-wait time.
Second, the authentication delay occurs while an exchange of Authentication frames is made. The authentication includes two or four consecutive frames according to an authentication method used by the AP. Several wireless Network Interface Cards (NICs) attempt re-association before the authentication. However, the attempted re-association causes an additional delay in the handover process.
Third, the re-association delay occurs while an exchange of Re-association frames is made. If the Authentication phase is successfully achieved, the mobile station sends a Re-association Request frame to the AP and receives a Re-association Response frame in response to the request. This completes the handover. Meanwhile, the inclusion of the IAPP phase additionally required between the new AP and the other APs will further increase the re-association delay.
The mobile station suffers multiple delays in the process of performing handover between APs in the conventional WLAN. This affects the quality of service (QoS) and makes it impossible to perform fast handover.
Accordingly, there is a need for an improved system and method for providing a re-association method for minimizing a service delay due to handover in a WLAN mesh network.